X-ray image viewer

ABSTRACT

An X-ray viewer for coloured radiographic images. The apparatus comprises two groups of light sources with different colour temperature. The current through the groups can be progressively varied so as to increase or decrease the amount of irradiating light which lies in part of the visible spectrum which is complementary to the predominating wavelength in the image colour. The variation in the spectral composition causes no substantial change in the illumination of the image.

United States Patent 11 1 De Belder el; al.

1 1 Mar. 12, 1974 1 X-RAY IMAGE VIEWER 3,217,594 11/1965 Simmon 355 35 xH 3,227,044 l/l966 Hunt e1 aln. 350/3]? X lnvcmo Maunce 3,322,025 5/1967Dauscr 355/35 x Mcchelcn; Bone", 3,627,908 12/1971 Dziilcy 355/37 xHove; Luc Yves Natens, Berehem, 2,885,564 5 1959 Marshall, Jr. 307 299all Of Belgium 3,198,980 8/1965 Martin 3l5/l5l X 9 5 [73] Ass1gnee:Agfa-Gevaert N.V., Mortsel, 3 247 390 4/1 66 Kim! 315/] l X BelgiumPrzmary Exammer-Nathan Kaufman Filedi J 12, 1971 Attorney, Agent, orFirmWilliam J. Daniel [21] Appl. No.: 105,923

[57] ABSTRACT [30] Foreign Application Priority Data An X-ray viewer forcoloured radiographic images, Jan. 12, 1970 Great Britain 1469/70 The ppComprises two groups of light sources with different colour temperature.The current 52 us. (:1 315/151, 355/37, 315/312 through the groups canbe progressively varied so as 51 Int. (:1. 1105b 37/02 to increase ordecrease the amount of irradiating light 58 Field 01 Search 315/151;355/37, 35, 113, which lies in P2111 of the visible spectrum which is355 complementary to the predominating wavelength in the image colour.The variation in the spectral compo- 5 References Cited sition causes nosubstantial change in the illumination uwmzo STATES PATENTS 0f the3,110,761 11/1963 Allen at al. 355/35 X 4 Claims, 4 Drawing Figures 28{1 BIDIRECTIONAL WHITE RECTIFIER LIGHT CONTROL MODULE BIDIRECTIONALRECTIFIER CONTROL MODULE PAnzminummn 3.798.916

sum 1 or 4 Fig. 7

PATENTEB "AR 1 2 I974 SHEET 3 OF 4 X-RAY IMAGE VIEWER This inventionrelates to light projection apparatus for use in recording or viewingtransparent coloured photographic and radiographic images.

If a said transparent image consists of or includes juxtaposed areas ofthe same colour but different colour density, the image detailsrepresented by the colour density difference are sometimesinsufficiently clear when the image is recorded or viewed by means oftransmitted light.

It is an object of the invention to provide for modification of thevisual contrast of such images.

According to the present invention, a light projectin apparatus is usedfor projecting light through a transparent coloured image having atleast one part which comprises juxtaposed areas of the same image colourbut different colour density, said apparatus comprising a diffusingscreen, a light source or light sources arranged for illuminating saidscreen substantially uniformly, means whereby the spectral compositionof the light irradiating the screen can be progressively varied over avariability range at one end of which the irradiating light lies in thatpart of parts of the visible spectrum which is or are complementary tothe part or parts of such spectrum containing the wavelengths or thepredominating wavelengths forming the irradiating light at the other endof such range, and means which maintains the illumination of the screensubstantially constant during such variation of the spectral compositionof the irradiating light.

In the foregoing definition, the term image colour means the colour ofthe light transmitted by the image or image part in question when it isirradiated with white light, and the term irradiating light means thelight incident upon the specified image or image part.

In order to permit the visual contrast to be increased to an appreciableextent it is preferred to design the system so that an one end of thevariability range the composition of the irradiating light is at leastmainly in the said complementary part of parts of the visible spectrum.Optimally, at that end of the variability range the composition of theirradiating light is entirely of substantially entirely in suchcomplementary part or parts of the spectrum. In order to achieve a widecontrast variability range it is preferred to design the system so thatat the other end of the variability range the amount of irradiatinglight which lies in said complementary part or parts of the visiblespectrum is nil or substantially so, or at least is less than the amountof irradiating light which is in the other part or parts of the visiblespectrum.

For the purposes primarily in view it is important for the controlsystem to be designed so that the progressive variation in the spectralcomposition of the irradiating light can be instantly terminated at anypoint within the total variability range.

The variation in the spectral composition of the irradiating light can,e.g., be achieved by using light sources the light emissions of whichare wholly or mainly in different spectral bands and can besimultaneously varied in intensity in opposite sense, or by means ofdifferently coloured light-reflecting surfaces which are displaceableand/or can be selectively masked for achieving the required variation inspectral composition in respect of the total reflected light, this beingused for irradiating the transparent image.

The illumination of the image or image part which is subject to visualcontrast variation may be kept constant during such variation by meansof at least one photosensitive device influencing the output of thelight source or light sources in response to any variation in theintensity of the irradiating light.

As the invention has been made primarily with a view to aiding theinspection of transparent monochrome or polychrome images, andparticularly monochrome X-ray images, the invention will be hereinafterdescribed more specifically in that context. it will be evident howeverthat if a given modification of the spectral composition of theirradiating light improves the visual contrast of the image, the samemodification will enable the image details to be recorded with improvedcontrast if the transmitted light is used for recording or copying theimage onradiation-sensitive material.

In order to achieve a substantially homogeneous spectral composition ofthe irradiating light for all settings within the variability range itis desirable to interpose a light mixing device or devices between thelight source or sources and the transparent image. For viewingtransparent images by transmitted light it is preferred to use a lightmixing device in the form of a diffusing screen. Preferably theapparatus employed includes means for holding a said transparent imageagainst the diffusing screen.

The apparatus employed may be designed for illuminating the whole of anexposed and developed film or plate as conventionally used in medicalradiography or for illuminating two or more such films or platessimultaneously. The means for varying the spectral composition of theirradiating light can be effective over the whole of the viewing area orover only a limited zone within that area. In the latter case the visualcontrast of any selected part of an image can be varied provided thefilm or plate is located with that part of the image in the variabilityzone. One or more shutters or masks may be provided for masking any partof an image which at any given time does not need to be inspected.

Depending on the extent of the viewing area over which the contrastvariability is to be effective it may be desirable to provide aplurality of light sources in a plane substantially parallel with theviewing plane (the plane of the irradiated image). For illuminating agiven viewing area substantially uniformly, the depth of the spaceoccupied by the apparatus, measured from the viewing plane to the lightsources can then be small in comparison with the depth of space requiredif only one light source is used.

As applied to monochrome radiographic image viewing systems, theinvention gives particularly good results in the case that theradiographic image is in the blue-cyan colour range and the irradiatinglight can be varied over a range at one end of which the irradiatinglight is composed wholly or predominantly of wavelengths within the saidrange blue-cyan, e.g., is substantially the same colour as the image oris of neutral colour, and at the other end of which variability rangethe irradiating lightis wholly or mainly composed of wavelengths in aband or bands of the spectrum complementary to the band or bandscontaining the wavelengths or the predominating wavelengths in the saidimage colour; for example at the said other end of the variabilityrange, the irradiating light may be yellow or in the orange-red colourrange. When the irradiating light is in that colour range the visualcontrast of the irradiated image is improved, particularly in the caseof low density areas.

An apparatus for carrying out the invention will now be described withreference to the accompanying diagrammatic drawings.

FIG. 1 is a diagrammatic view of an apparatus according to theinvention.

FIG. 2 is the electronic circuit for controlling the apparatus accordingto FIG. 1.

FIG. 3 shows a circuit for controlling the current through tubes V1 toVII.

FIG. 4 shows a power supply for the circuit of FIG. 3.

FIG. 1 shows a radiographic film viewer comprising a housing 10, aplurality of parallel electroluminescent gas discharge tubes 17 and 18,a diffusing screen 12, a clip 13 fitted to the housing of the apparatusfor holding a radiographic film sheet 14 against the screen, anelectronic control circuit 15 located in the lower part of the housing,and a remote control 16 with a first knob for setting theoverall-luminance of the viewer and a second one for controlling thespectral composition of the light.

The electroluminescent tubes are divided into two arrays, one arraycomprising the tubes 17 and the other array comprising the lamps 18. Thetubes 17 produce white light of high colour temperature whereas thetubes 18 are in fact the same kind of tubes with low colour temperaturewhich additionally are provided with a tubular envelope 19 formed by atriacetate sheet on which an orange filter layer has been coated.

The electronic circuit 15 for controlling the tubes is showndiagrammatically in FIG. 2. It comprises the arrays of tubes 17 and 18,each tube having its own choke 20 in series therewith, the controlmodules 21 and 22, the bi-directional SCR 23 and 24, the potentiometers-26 and 27 which are located in the remote control box 16 which isconnected through a flexible cable with the electronic circuitry, and aconnection 28 to an AC. mains supply.

The apparatus comprises also a mains transformer, not shown in thedrawing, having a plurality of secondary windings onto which thedifferent filaments at one side of the discharge tubes are connectedindividually, The filaments at the other side of the tubes may beconnected in parallel to one secondary winding of the transformer. Thevoltage of one secondary of the transformer is rectified, stabilised,and used as a DC. potential from which the adjustment potential for thecontrol modules is derived by means of the potentiometers 25-26 and 27.

The control modules 21 and 22 provide a pulsating output signal fordriving the bi-directional SCR 23 and 24 into the conductive state, thewidth of the pulses of the signal being proportional to the magnitude ofthe DC potential applied to the input of the control modules.

The input voltage of the control modules, and thus the luminance of allthe tubes, is in the first place determined by the setting of thepotentiometer 27, since a variation in the said setting influences inthe same sense the two control modules.

In a second way, the input voltage of the modules is determined by thesetting of the potentiometers 25 and 26 which are mechanically coupledwith each other, and which are electrically connected in such a way thatthe output voltage at one slider decreases in correspondence with anincrease of the voltage at the slider of the other potentiometer. In thementioned way, a change in the luminance of the tubes 17 is alwaysopposite to a change in the luminance of the tubes 18, and thus thepotentiometers 25 and 26 permit to change the spectral composition ofthe produced radiation gradually from white to orange, the overallluminance of the irradiating light remaining substantially constant.

Although the behaviour of the bi-directional SCR in connection with thecontrol modules is not strictly linear and the light output of the tubesis also not a strict linear function of the applied current, it has beenshown that deviations of the overall luminance of the irradiating lightremain within 10 percent. A deviation of this order of magnitude is notperceptible for the operator working with the apparatus, and thereforeno ad ditional correcting means is required to keep the luminanceconstant Within closer limits.

However, the parallel connection of the electroluminescent tubes cangive rise to non uniform luminance distribution, especially whenoperating them at low light levels.

In case it is yet required to keep the luminance constant within closelimits, or if the spectral composition of the two groups of tubes issuch that the impression of a constant luminance cannot be obtained, aphotoelectric cell may be provided which measures the luminance of theviewing screen or of a part thereof and which controls the overallluminance of the tubes. In a most simple embodiment, a photodiode may beinserted in series between the potentiometer 27 and the ground, so thata decreased light output causes the resistance of the photocell toincrease and thereby the potential at the slider of the photentiometerto increase correspondingly, and vice versa.

In FIG. 3 is shown an improved electronic circuit for controlling thecurrent through electroluminescent tubes V1 and VII. The tubes aredivided into two groups, the tubes of each group now being fed inseries, so that the light intensity is uniform all over the viewer.Indeed, the light emission of an electroluminescent tube is primarilydependent on the temperature of/and the current through the tube. Sixtubes Vii, V3, V, V7, V9 and VII, e.g. of the commercially availableSylvania lamp type F 15 T 8-WW are used which emit light in theorange-red colour range. These lamps are tubelike low pressure mercurylamps with a nominal power of 20 W and a low equivalent colourtemperature. AL ternately to said tubes five further tubes V2, V4, V6,V8 and V10 of the type F 15 T 8-D also commercially available fromSylvania, are positioned having same sizes and nominal power as theforegoing tubes however with a high equivalent colour temperature.More-- over, tubelike selective filters which e.g. absorb allwavelengths under 570 nm are provided around the tubes V1, V3, V5, V7,V9 and V11.

To avoid disturbing ripple on the light flux of the tubes at lowfrequency, say in the order of magnitude of 50-lOO Hz, the tubes are fedwith DC pulses of 540 V at e.g. 16 kHz so that equally no nuisanceoriginating from disturbing acoustical noise effects is encountered. Thewidth of the pulses is modulated according to the desired luminous fluxas will be further exposed hereinafter.

Since the tubes are fed with DC. only the cathode filament of each tubehas to be heated. As the cathodes of the various tubes have differing DCpotentials the cathode filaments of the tubes are each fed by anindividual winding on a high-frequency transformer which is itself fedby a separate transistor oscillator of e. g. the balanced convertertype. The diagram of FIG. 4 shows the heater current transformer Trl.Here the heater current windings are formed by three windings ofconnecting wire around the ferrite core of the transformer Trl.

On the tubes V1 and V11 ignition strips are provided which asillustrated in FIG. 4 are connected via a capacitor with the so-calledhot side of the A.C-mains terminals. For assuring the ignition of theset of tubes V1, V3, V5, V7, V9 and V11 the anode of tube V7 isconnected with the 540 V terminal over a resistor R1 in the order ofmagnitude of 1 M Q. Hence full voltage is given to the tubes V11, V9 andV7 at the ignition, so that these three tubes will positively ignite.Thereupon tubes V5, V3 and V1 will ignite quite safely.

The DC-voltage of 540 V may be obtained in a very simple way by doublingthe AC-voltage of 220 V by means of a diode-capacitor pump circuit.Occasionally said voltage may be stabilized by means of a siliconcontrolled rectifier (SCR). In case of a l 17 V-AC mains a voltagequadruplication may be applied. For 2 reaons of safety the low voltageis obtained by means of a transformer Tr2.

The control circuitry of each of the coloured light sources of theviewer system, consists essentially of a set of potentiometers,determining the desired colour and/or luminance, of a measuringphotocell resistor bridge, a PID controller, a pulse width modulator anda switching power regulator, feeding current to the respective groups oftubes. The photocells are biased through current sources T2 and T3.Their current value is given by the voltage drop over forward biaseddiodes D1, D2, D3, the presence of which will be referred to later on.

The control errors are measured between the nodes of two bridges thefirst one consisting of LDRl, T2 and the potentiometric dividercontaining P3, the second one consisting of LDRZ, T3 and the samepotentiometric circuit. The errors are fed to the operational amplifiers,uA 70 1 /2 connected onto a filj controller mode. if i The outputsignal of the ,41A 709 1/2 is further com pared with the output signalof a miller-integrator T5 delivering a sawtooth voltage. Themiller-integrator is fed with a constant current i which is derived fromthe balanced converter of FIG. 4. In this way the millerintegrator onlyruns when the filaments are heated. The capacitor C is periodicallydischarged through the unijunction transistor T4 delivering needlepulses with a frequency of e.g. 20 kHz. The comparator transistors tilt/deliver pulses which are modulated in width by the output signal of the,uA 709 1/2. These pulses are further amplified by the transistors T8/T9and passed through a transformer Tr3/Tr4 to the basis of high voltagetransistors TlO/Tll which control the current through the seriesconnection of the tubes V1, V3, V5, V7, V9 and Vii/V2, V4, V6, V8, V10.Further a choke L1/L2 in series connected with said tubes is arrangedfor maintaining the current passing through the tubes to a substantiallyconstant value and between the emitter of TlO/Tll and the negativeterminal of the high voltage source (-540 V) a free wheel diode D4/D5 isconnected which is conductive during the moments transistor TlO/Tll isblocking.

Resistor LDRl and LDR2 and potentiometer P1 and P2 are thus measuredthat the subjective contrast of a standard transparency varies linearlyas a function of the angular position of P2.

The layout of the circuit is so that rotating the potentiometer axis inone direction increases the light intensity of one series connection oftubes and decreases at the same time the light intensity of the otherseries connection.

The base drivers of the current sources T2 and T3 are determined by theforward voltage drop accross the diodes D1 to D3. This voltage drop istemperature dependent and compensates for the temperature coefficient ofthe photoresistors. Said voltage drop determines the emitter voltage ofT1 and thereby the base currents of T2 and T3.

The total light intensity can further be set by means of P3 which isconnected between the terminals of the low voltage supply 18 V). Theslider of this potentiomet rcgrmgtedto the reference inputs of theoperational amplifiers ;.LA 709 lI? respeaivelyfThe total light emissionof both groups of tubes is made independent of the setting of thepotentiometers P2 and P3 by choosing the correct component values.

Various other forms of apparatus can be used for carrying out theinvention. For example, the required colouration of the colouredreflecting surfaces and the colour variation can be achieved bydisplacing, e.g. pivoting, such surfaces in relation to the light sourceor sources, or by providing one or more movable reflectors which can bedisplaced in relation to the light source or sources for directing lightfrom such source or sources onto one or another of such reflectingsurfaces or onto both or all of them in predetermined proportionsdetermined by the position of the reflector or reflectors. Such colouredreflecting surfaces may be, e.g., inner surfaces of the housing or lampbox.

While the viewing of monochrome images has been more particularlyreferred to, it will be apparent that the invention can be usefullyapplied in systems for viewing polychrome images. By providing lightsources emitting irradiating light in different spectral bandscomplementary to those of the different image colours and enabling suchdifferent light sources to be used in dependently, the contrast withinimage areas of any given colour can be enhanced at will by switching tothe appropriate colour of irradiating light.

We claim:

1. Light projecting apparatus for projecting light through a transparentimage having a color predominantly within a given region of the visiblespectrum and composed at least in part of juxtaposed image areas inwhich said color varies in color density, said apparatus comprising:

a. two groups of electro-luminescent tubes, one group emitting light ina first spectral region con taining the predominant color region of saidimage and the other group emitting light in a second spectral regionsubstantially complementary to said predominant color region of saidimage,

b. a diffusing screen for mixing the light emitted by said two groups oftubes to illuminate the said transparent image substantially uniformly,

c. means for progressively varying the electric currents through therespective two groups of tubes in inverse proportion to one another tothus progressively vary the spectral composition of said illuminatinglight between said first and said second spectral region, and

d. means for controlling the overall intensity of the emitted light tokeep the intensity of illumination of the transparent imagesubstantially constant independently of the variation of the spectralcomposition of the illuminating light between said first and said secondspectral region.

2. Light projecting apparatus according to claim 1 comprising at leastone photoelectric cell for measuring the intensity of the emitted lightand for controlling the current through at least one group ofelectroluminescent tubes to keep the overall intensity of the emittedlight substantially constant.

3. Light projecting apparatus according to claim 2 comprising a controlamplifier with differential inputs, one input receiving an electricsignal corresponding with the setting of said means for progressivelyvarying the electric current through the two groups of tubes,

I and the other input receiving an electric signal corresponding to apredetermined level of overall intensity of illumination.

4. Light projecting apparatus according to claim 3 comprising anelectric circuit for producing an electric signal having a saw-toothpattern, and means for comparing said saw-tooth signal with the outputsignal of said controlling amplifier, the electric signal resulting fromsaid comparison controlling an amplifier stage which produces a pulsewidth modulated output signal for controlling the current through saidelectroluminescent tubes, the frequency of said output signalcorresponding with the frequency of said sawtooth sig nal, and the pulsewidth of said output, signal depending on said electric comparisonsignal. k =0: :v

1. Light projecting apparatus for projecting light through a transparentimage having a color predominantly within a given region of the visiblespectrum and composed at least in part of juxtaposed image areas inwhich said color varies in color density, said apparatus comprising: a.two groups of electro-luminescent tubes, one group emitting light in afirst spectral region containing the predominant color region of saidimage and the other group emitting light in a second spectral regionsubstantially complementary to said predominant color region of saidimage, b. a diffusing screen for mixing the light emitted by said twogroups of tubes to illuminate the said transparent image substantiallyuniformly, c. means for progressively varying the electric currentsthrough the respective two groups of tubes in inverse proportion to oneanother to thus progressively vary the spectral composition of saidilluminating light between said first and said second spectral region,and d. means for controlling the overall intensity of the emitted lightto keep the intensity of illumination of the transparent imagesubstantially constant independently of the variation of the spectralcomposition of the illuminating light between said first and said secondspectral region.
 2. Light projecting apparatus according to claim 1comprising at least one photoelectric cell for measuring the intensityof the emitted light and for controlling the current through at leastone group of electro-luminescent tubes to keep the overall intensity ofthe emitted light substantially constant.
 3. Light projecting apparatusaccording to claim 2 comprising a control amplifier with differentialinputs, one input receiving an electric signal corresponding with thesetting of said means for progressively varying the electric currentthrough the two groups of tubes, and the other input receiving anelectric signal corresponding to a predetermined level of overallintensity of illumination.
 4. Light projecting apparatus according toclaim 3 comprising an electric circuit for producing an electric signalhaving a saw-tooth pattern, and means for comparing said saw-toothsignal with the output signal of said controlling amplifier, theelectric signal resulting from said comparison controlling an amplifierstage which produces a pulse width modulated output signal forcontrolling the current through said electro-luminescent tubes, thefrequency of said output signal corresponding with the frequency of saidsawtooth signal, and the pulse width of said output signal depending onsaid electric comparison signal.